1. Technical Field
The present invention relates to a type of phosphors, and more particularly, to a type of phosphors for use in white-light lighting apparatuses.
2. Description of Related Art
Semiconductor lighting apparatuses include light-emitting diodes (LEDs) and laser diodes. Semiconductor lighting apparatuses which provide ultraviolet or near-ultraviolet light can be used in combination with different phosphors to make various kinds of light sources.
Of all the new products in the LED industry, white light-emitting diodes are the most promising ones because they provide such advantages as having small sizes, low heat generation, low power consumption and long service life. Therefore, white light-emitting diodes can be used to replace fluorescent lamps and back lights of flat-panel displays. The so-call “white light” is in fact a combination of colored lights having various wavelengths. A white light visible to the human eyes must comprise a combination of lights of at least two colors, such as a combination of blue and yellow lights or a combination of green, blue and red lights.
Presently, most of the commoditized white-light lighting apparatuses generate a white light by using blue LED to convert yellow-emitting phosphor powder of Y3Al5O12:Ce (YAG:Ce) into a white light. This commoditized yellow-emitting phosphor powder is prepared through a solid-state sintering reaction at a high temperature ranging from 1400° C. to 1600° C., and can be excited by a blue LED having an emission wavelength of 467 nm to produce a yellow light having an emission wavelength of 550 nm, whose CIE chromaticity coordinates are (0.48, 0.50).
This yellow-emitting phosphor powder for use with a blue LED is synthesized under strict conditions, e.g., through a solid-state sintering reaction at a relatively high temperature, and emits a light that lacks a blue light component, so as to show a poor color-rendering property when used in a white-light lighting apparatus.